1. Field of the Invention
The invention relates to a cage used in a thrust roller bearing that supports, for example, a crushing portion of a crusher so that the crushing portion is rotatable, and to a thrust roller bearing including the cage.
2. Description of the Related Art
In a crusher that crushes solids such as rocks or stones, a thrust roller bearing is used. The thrust roller bearing supports an umbrella-shaped crushing portion so that the crushing portion is rotatable. Although a large crushing load is applied to the crushing portion, a full complement roller bearing, whose loading capacity is large, cannot be adopted as the thrust roller bearing that supports the crushing portion, for the following reason. Since the crushing portion rotates at a high speed, if the full complement roller bearing is used, skew occurs.
Thus, a thrust roller bearing as described above includes a cage that maintains each circumferential interval between rollers adjacent to each other. An example of the cage employed is a machined cage made of brass that is integrally constituted by a large-diameter annular portion, a small-diameter annular portion concentric with the large-diameter annular portion, and a plurality of bar portions each of which extends along the radial direction and connects the large-diameter annular portion and the small-diameter annular portion. In the machined cage, each bar portion is interposed between rollers adjacent to each other, so as to maintain the circumferential interval between the rollers.
Further, a pin-type cage 105 as shown in FIG. 4 may be employed. The pin-type cage 105 includes, instead of the above-described bar portions, bar portions (pins) 152 each of which is inserted in a through-hole 104h extending along a rotation central axis 104r of a roller 104, and connects a large-diameter annular portion 151 and a small-diameter annular portion 156. In the pin-type cage 105, each bar portion (pin) 152 inserted through the roller 104 maintains the circumferential interval between the rollers 104. Thus, the pin-type cage 105 is able to retain a large number of rollers 104 between a fixed ring 102 and a rotary ring 103, as compared to the machined cage. As a result, the pin-type cage 105 has an advantage that the loading capacity can be increased.
A large crushing load is unevenly applied to the crushing portion of the crusher described above under a severe vibration environment due to the crushing operation. Therefore, a large load may be locally applied to one or more of the rollers 104 provided in a thrust roller bearing 101 that supports the crushing portion. Thus, the one or more of the rollers 104, to which the large load is applied, roll less easily than the rest of the rollers 104. As a result, the large load in the circumferential direction is applied to the bar portion (pin) 152 that retains each of the one or more of the rollers 104 so that the roller 104 is rotatable, and accordingly, the bar portion (pin) 152 is likely to break. Further, the crushing portion of the crusher is a consumable part and is therefore periodically replaced. When the crushing portion is replaced, an inspection operation and a maintenance operation for the bearing can be performed. It is desirable that components of the bearing can be easily replaced when the inspection operation and the maintenance operation are performed.